1. Field of the Invention
The present invention relates to a radiation treatment apparatus having a radiation generating unit, which is movable around an object of radiation, and applying radiation to the object of radiation in multiple directions.
2. Description of the Related Art
For example, a radiation treatment apparatus for use in radiation treatment comprises a linear accelerator for generating radiation and a positioning device for passing the radiation, which is emitted from the linear accelerator, through an object of radiation in multiple directions.
There is a radiation treatment apparatus having as a positioning device a gantry that is rotatable about a horizontal axis. A linear accelerator is disposed within the gantry. Radiation is emitted from an end portion of the gantry toward the center of rotation. In this radiation treatment apparatus, when the gantry is rotated and radiation is emitted, radiation crosses at one point. Hence, this apparatus is called an isocentric type apparatus. An object of radiation is positioned at an isocenter.
In addition, there is a radiation treatment apparatus having a multi-axis manipulator as a positioning device. A linear accelerator is attached to the head of the multi-axis control manipulator. In this radiation treatment apparatus, when the manipulator is moved and radiation is emitted, radiation does not cross at a specified one point. Thus, this apparatus is called a non-isocentric type apparatus. An object of radiation is positioned within a range of movement of the manipulator.
In the radiation treatment apparatus having the gantry as the positioning device, the direction of application of radiation is varied only by the rotation of the gantry. Consequently, in order to apply radiation in a direction other than the direction of application of radiation that is varied by the rotation of the gantry, the object of radiation needs to be rotated about an axis at an angle different from the angle of the rotational axis of the gantry.
In particular, in radiation treatment, the object of radiation is within the body of a patient and thus the patient has to be rotated about the isocenter in order to rotate the object of radiation. In this case, the patient is inclined with respect to the isocenter, except the case where the patient is rotated about a vertical axis. As a result, the attitude of the patient or the shape of a diseased part may vary due to an external factor such as gravity.
In the radiation treatment apparatus having the multi-axis control manipulator as the positioning device, the direction of application of radiation can be set at a desired angle around the object of radiation by controlling each axis of the manipulator. Even when the direction of radiation is the same, the attitude of the manipulator is various and not singular. The bending of the manipulator and the load acting on each axis vary depending on the attitude. Consequently, it is difficult to precisely position the head that emits radiation. Moreover, the adjustment of position of the head is complex, and the reproducibility of the angle of application of radiation is low.
In these conventional radiation treatment apparatuses, the radiation cannot precisely be applied, and thus the amount of radiation on parts other than the object of radiation increases.
Under the circumstances, there is a demand for a radiation treatment apparatus that can apply radiation in multiple directions without inclining the object of application of radiation and has high reproducibility of the angle of application of radiation.